Magnetic inhibition of the recollimation instability in relativistic jets

TL;DR

This study uses 3D relativistic magnetohydrodynamic simulations to show that even weak azimuthal magnetic fields can fully suppress recollimation instabilities in AGN jets, impacting their morphology.

Contribution

It demonstrates that a weak magnetic field can prevent recollimation instability, linking it to centrifugal instability and providing insights into AGN jet behavior.

Findings

Weak magnetic fields suppress recollimation instability

Recollimation instability is linked to centrifugal instability

Results relate to AGN jet morphology and Fanaroff-Riley classification

Abstract

In this paper, we describe the results of three-dimensional relativistic magnetohydrodynamic simulations aimed at probing the role of regular magnetic field on the development of the instability that accompanies recollimation of relativistic jets. In particular, we studied the recollimation driven by the reconfinement of jets from active galactic nuclei (AGN) by the thermal pressure of galactic coronas. We find that a relatively weak azimuthal magnetic field can completely suppress the recollimation instability in such jets, with the critical magnetisation parameter $\sigma_{cr} < 0.01$. We argue that the recollimation instability is a variant of the centrifugal instability (CFI) and show that our results are consistent with the predictions based on the study of magnetic CFI in rotating fluids. The results are discussed in the context of AGN jets in general and the nature of the Fanaroff-Riley morphological division of extragalactic radio sources in particular.